Presentation data read from a digital video disc (DVD) can include video, audio and subpicture data multiplexed with navigation data in conformance with the MPEG-1 or MPEG-2 program stream specification. The video data exists as one stream of data compressed according to the MPEG-1 or MPEG-2 video format. The video data is generally stored on the DVD with a 420 video format.
Subpicture data can consist of data such as subtitles, menus, karaoke lyrics, etc. that can be overlaid as a bitmap onto the main video content. The subpicture data is compressed using run length encoding. Subpicture data is stored in a 444 chroma format using a 16-color lookup table. When the subpicture data is run-length decoded, a color index (e.g., a 4-bit index mapping to a table holding 16 different colors, each specified with luminance and chrominance (e.g., Y, Cr and Cb) values) is obtained.
Referring to FIG. 1, a system 10 is shown illustrating a conventional DVD playback scheme. The system 10 includes a DVD demultiplexer block 12, a video decoder 14, a subpicture decoder 16, an audio decoder 18, an upsampling block 20, a subpicture compositing block 22, a video presentation block 24 and an audio presentation block 26. The DVD demultiplexer block 12 receives a presentation data signal (i.e., IN) from a recorded disc 30. The DVD demultiplexer block 12 demultiplexes the signal IN to retrieve the video data signal (i.e., V), the subpicture data signal (i.e., SP) and the audio data signal (i.e., A). The video decoder 14 processes the signal V and presents a signal (i.e., V1) to the upsampling block 20. The upsampling block 20 performs a 420 format to 422 format upsampling routine to generate a signal (i.e., V2). The subpicture decoder 16 converts the subpicture signal SP to a subpicture signal SP1. The subpicture signal SP1 is in the 444 16-color lookup table format. The subpicture compositing block 22 combines the signal V2 (i.e., the 422 format video signal) with the signal SP1 to generate a composite 422 format chroma signal (i.e., V3).
The video presentation block 24 presents the video images in response to the signal V3. The audio decoder 18 presents a signal A1 to the audio presentation device 26. The audio presentation device 26 presents audio signals, through devices such as loudspeakers, in response to the audio signal A1.
The conventional DVD playback scheme of compositing the 422 chroma format main picture information and the 444 16-color lookup table subpicture information uses a large amount of memory space and a large amount of DMA bandwidth. A large amount of memory and DMA bandwidth add to the expense of the DVD playback system. It would be desirable to reduce the amount of memory and DMA bandwidth used in a DVD playback system.